I’m a big fan of Jumble builds. I like to try to put the bits I’ve accumulated to use.
Key question, do you really like using friction shifting and down tube mounting, or are you just curious to try them? I prefer indexed shifting and brifters, thumbshifters or bar end mounting over down tube mounts. If you have a shifter with both modes you can often switch to friction mode if you prefer it. Nice to have the option imho.
I think 7, 8 and 9 speed are still good, reliable choices. I think 1x is a fad at present, that notwithstanding, if it covers the gear range you need then why not.